1. Field of the Invention
The invention relates to a vehicular motion control apparatus and a vehicular motion control mode. More specifically, the invention relates to a vehicular motion control apparatus and a vehicular motion control method for controlling motion of a vehicle using a steering angle detected by a steering angle sensor.
2. Description of the Related Art
According to a vehicular motion control apparatus for an automobile or the like as a known example, a target behavior of a vehicle is calculated at least on the basis of a detected value of a steeling angle relative to a neutral position of a steering wheel, and motion of the vehicle is controlled in accordance with a difference between a target value of the behavior of the vehicle and an actually measured value of the behavior of the vehicle. In this apparatus, If the neutral position of the steering wheel has not been detected, a steering angle is estimated from a steering angle stored during the last off-period of an ignition switch and a cumulative value of the number of pulses delivered from a steering angle sensor after the turning of the ignition switch, so as to control motion of the vehicle. This vehicular motion control apparatus is disclosed, for example, in Japanese Patent Application Laid-Open No. 10-287262.
In the aforementioned vehicular motion control apparatus, however, a means for storing a steering angle during the last off-period of the ignition switch is required. Also, if a driver operates the steering wheel to cause a change in steering angle before the ignition switch is turned on and aft the ignition switch has been turned off, it is impossible to precisely detect a steering angle. This causes a problem in that motion of the vehicle cannot be controlled suitably.
There is also known a method of detecting on the basis of a yaw rate or the like of a vehicle that the vehicle is traveling straight on at a constant speed, and calibrating a neutral point of a steering angle sensor when the vehicle is traveling straight on at a constant speed. In the case of this method, however, there is a problem in that the neutral point of the steering angle sensor cannot be calibrated unless it is detected that the vehicle is traveling straight on at a constant speed.